Method of manufacturing aluminum alloy

ABSTRACT

The present disclosure relates to a method of manufacturing an aluminum alloy with excellent mechanical properties by controlling a heat treatment step and a cooling step in a process of manufacturing the aluminum alloy. In detail, there is provided a method of manufacturing an aluminum alloy, including: a heating step of heating an aluminum alloy made of an aluminum alloy composite up to 500 to 560° C.; a solution treatment step of maintaining the heated aluminum alloy for 5 to 7 hours; a cooling step of cooling the solution-treated aluminum alloy for 15 seconds to 1 minute; and an aging step of age-hardening the cooled aluminum alloy for 2.5 to 4 hours at 140 to 180° C.According to the method of manufacturing an aluminum alloy of the present disclosure and an aluminum alloy manufactured by the method, elongation is secured by reducing the solution treatment time and strength is increased by remaining heat by relatively increasing the drop speed of a pallet between a solution treatment furnace and a cooling container, the distance between the furnace and the container, and the cooling time, thereby being able to provide an aluminum alloy having excellent mechanical properties.

TECHNICAL FIELD

The present disclosure relates to a method of manufacturing an aluminum alloy and, more particularly, to a method of manufacturing an aluminum alloy with excellent mechanical properties by controlling a heat treatment step and a cooling step in a process of manufacturing the aluminum alloy.

BACKGROUND ART

Aluminum (Al) is easy to mold, is easy to process at room temperature or high temperature when alloyed with another metal, has high anticorrosion in the atmosphere, and has high electrical and thermal conductivity, so it is widely used throughout the industry.

Heat treatment that combines heating and cooling in various types is used to give general properties such as strength, hardness, wear resistance, impact resistance, and processability that are required for metal or alloys. Such heat treatment uses recrystallization of metal or an alloy, diffusion and phase transformation of atoms, etc.

That is, such heat treatment is generally used to increase the strength or hardness of metal materials or to remove internal stress and improves the properties of materials or gives specific properties by controlling the temperature, time, speed, etc. of heating or cooling. Quenching, tempering, annealing, normalizing, etc. are included in such heat treatment.

In particular, aluminum is very light and has excellent processability, anticorrosion, and thermal and electrical conductivity, but has low strength in comparison to other metals, so it is difficult to use aluminum as pure metal. Accordingly, depending on uses, aluminum is alloyed or heat treatment is applied to some aluminum alloys to increase strength and hardness or reduce or remove stress. In general, since aluminum alloys have a reinforcing phase component, it is possible to improve the properties such as improving strength and hardness and removing stress through heat treatment, but a defect may be caused, depending on methods.

Although such a defect is insignificant and does not have a great influence in a general operation environment, there is a problem that a defect is magnified or generated when temperature is increased due to heat treatment, etc. In order to prevent defects and improve properties in such a heat treatment process, studies for improving the structural design of heat treatment apparatuses have been conducted, as in Korean Patent Application Publication No. 10-2018-0069268.

Further, other than mechanical characteristics, heat treatment temperature and the following processes of aluminum alloys have an influence on the properties of the alloys, particularly, strength and elongation, so the conditions for a heat treatment step and an age-hardening step are also important. Accordingly, there is an increasing need for conditions in a process that satisfy the value of mechanical properties and a method of manufacturing an aluminum alloy that secures the conditions.

SUMMARY OF INVENTION Technical Problem

To satisfy the need described above, an objective of the present disclosure is to provide a method of manufacturing an aluminum alloy, the method controlling heat treatment and aging conditions.

Another objective of the present disclosure is to provide an aluminum alloy manufactured in accordance with the method of manufacturing an aluminum alloy.

Solution to Problem

In order to achieve the objective described above, the present disclosure provides a method of manufacturing an aluminum alloy, the method including: a heating step of heating an aluminum alloy made of an aluminum alloy composite up to 500 to 560° C.; a solution treatment step of maintaining the heated aluminum alloy for 5 to 7 hours; a cooling step of cooling the solution-treated aluminum alloy for 15 seconds to 1 minute; and an aging step of age-hardening the cooled aluminum alloy for 2.5 to 4 hours at 140 to 180° C.

The aluminum alloy may contain Sr. The cooling step may be performed for 15 seconds to 1 minute.

In order to achieve another objective, the present disclosure provides an aluminum alloy manufactured by the method of manufacturing an aluminum alloy of the present disclosure.

Advantageous Effects of Invention

According to the method of manufacturing an aluminum alloy of the present disclosure and an aluminum alloy manufactured by the method, elongation is secured by reducing the solution treatment time and strength is increased by remaining heat by relatively increasing the drop speed of a pallet between a solution treatment furnace and a cooling container, the distance between the furnace and the container, and the cooling time, thereby being able to provide an aluminum alloy having excellent mechanical properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a resultant graph showing tensile strength depending on the content of Sr in an aluminum alloy used in an embodiment of the present disclosure.

FIG. 2 is a resultant graph showing yield strength depending on the content of Sr in an aluminum alloy used in an embodiment of the present disclosure.

FIG. 3 is a resultant graph showing elongation depending on the content of Sr in an aluminum alloy used in an embodiment of the present disclosure.

FIG. 4 is a graph showing precipitation hardening according to the aging time of an aluminum alloy used in an embodiment of the present disclosure.

FIG. 5 is a graph showing hardness depending on a temperature difference in a solution treatment step of the present disclosure.

FIG. 6 is a graph showing hardness depending on a temperature difference in an aging step of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereafter, the present disclosure is described in detail.

According to an aspect of the present disclosure, there is provided a method of manufacturing an aluminum alloy, the method including: a heating step of heating an aluminum alloy made of an aluminum alloy composite up to 500 to 560° C.; a solution treatment step of maintaining the heated aluminum alloy for 5 to 7 hours; a cooling step of cooling the solution-treated aluminum alloy for 15 seconds to 1 minute; and an aging step of age-hardening the cooled aluminum alloy for 2.5 to 4 hours at 140 to 180° C.

In a heat treatment process, T6, which is a representative heat treatment method that is used for heat-treated aluminum alloys, is used to improve hardness and mechanical strength by precipitating a compound dissolved by solution treatment.

Though depending on the kinds and amounts of metals to be mixed and the shapes of parts to be used, a T6 heat treatment process improves strength and hardness of an aluminum alloy through steps of applying solution treatment to the aluminum alloy, performing quenching in water at room temperature, etc., and then performing aging treatment.

The method of manufacturing an aluminum alloy of the present disclosure performs heat treatment for a relatively reduced time in comparison to the heat treatment time in the related art in the heating and solution treatment steps. When the effect of the solution treatment increases, the expected level of an increase in strength increases but the expected level of elongation decreases. However, when the effect of the solution treatment decreases, the expected level of an increase in strength decreases but the expected level of elongation increases. Accordingly, the present disclosure has been made to solve the problem that elongation relatively decreases by reducing a solution time treatment to a predetermined level.

A solution-treated aluminum alloy undergoes a water or air cooling step. It is possible to cool a solution-treated aluminum alloy using high-temperature liquid, sprayed water, or the like. It is possible to cool a high-temperature aluminum alloy that has undergone a solution treatment step using liquid-state water at room temperature, using sprayed water such as fine drops, or using the atmosphere, but the present disclosure is not limited thereto.

The cooling step of the present disclosure is characterized by being performed for 15 seconds to 1 minute. It is possible to control the cooling time by adjusting the distance between a solution treatment furnace and a cooling container and the moving speed of an alloy pallet. Unlike rapid cooling in the related art, cooling is performed for a relatively considerable time, so strength can be secured by remaining heat. There is an effect that a predetermined level of strength and elongation of the manufactured aluminum alloy can be secured by reducing the solution treatment time and increasing the cooling time.

The aging step in the method of manufacturing an aluminum alloy of the present disclosure is characterized by age-hardening an aluminum alloy for 2.5 to 4 hours at 140 to 180° C. It is possible to adjust mechanical strength, particularly elongation, by controlling temperature and time that are processing variables of age-hardening.

Since there are differences in thickness and shape depending on the parts to which an aluminum alloy is applied, it is required to continuously measure and check the temperature of an entire part when performing heat treatment and aging steps according to the present disclosure, so it is preferable to accurately measure a temperature range, time, etc. using a thermo couple, etc.

The method of manufacturing an aluminum alloy of the present disclosure includes a solution treatment step and an aging treatment step, and one apparatus including exclusive furnaces and cooling containers can be configured. It is preferable to design the apparatus to satisfy a heat treatment reference by collecting and monitoring temperature generated by each apparatus through a DAQ module and making temperature uniform through calibration of a temperature controller.

As described above, due to the heat treatment process improved in comparison to the related art, it is possible to obtain an aluminum alloy having medium strength and high elongation that was difficult to secure through heat treatment in the related art, and it is possible to control the degrees of processes by adjusting the conditions of the processes.

The aluminum alloy that is used in the manufacturing method of the present disclosure may contain Sr. It is possible to improve elongation by increasing the cooling speed and adding Sr of 50 to 200 ppm. FIG. 1 is a resultant graph showing tensile strength depending on the content of Sr in an aluminum alloy used in an embodiment of the present disclosure, FIG. 2 is a resultant graph showing yield strength, and FIG. 3 is a resultant graph showing elongation.

Referring to FIGS. 1 to 3 , as for a change of tension characteristic after heat treatment depending on a cooling speed, it could be found that as the cooling speed increases, both the elongation (EL) and ultimate tensile strength (UST) increases. It was found that an ally of A356.2+50 ppm Sr with the content of Sr limited around 50 ppm was advantageous for securing the most excellent tensile strength and elongation throughout all cooling speeds. It could be found that the yield strength (YS) less depends on the cooling speed when the cooling speed is low, and the dependency slightly increases when the cooling speed increases.

The manufacturing method of the present disclosure is excellent in that it is possible to control the cooling time depending on the components of an alloy, and accordingly, to adjust strength and elongation, thereby securing excellent mechanical characteristics.

Preferred embodiments of the present disclosure are described in detail hereafter. Configurations, operations, and effects that those skilled in the art can easily know are simply or not shown and described, and parts related to the present disclosure are mainly described in detail.

Embodiment

Solution treatment temperature or aging temperature was adjusted to set optimal conditions for solution treatment and aging treatment. FIG. 4 is a graph showing precipitation hardening according to the aging time of an aluminum alloy used in an embodiment of the present disclosure, FIG. 5 is a graph showing hardness depending on a temperature difference in a solution treatment step of the present disclosure, and FIG. 6 is a graph showing hardness depending on a temperature difference in an aging step of the present disclosure. A process of setting a solution treatment temperature and an aging temperature is described hereafter with reference to FIGS. 4 to 6 .

Solution treatment was performed for 8 hours at 535° C. and then aging treatment was performed for a different time at 155° C. while minimizing a deviation in heat treatment temperature within ±5° C. for an A356.2 alloy in a small furnace to set a comparative reference, in which a peak-reaching time was checked by checking a precipitation hardening phenomenon according to an aging time.

Matrix hardness for every aging time was measured under load of 0.05 kg using a micro Vickers hardness tester, and as the result, it was found that peak hardness is reached around about 4 hours.

Considering a change in solution treatment temperature, it was found that the matrix hardness value was not greatly changed after aging when the solution treatment temperature was 515° C., which is lower by 20° C. than the reference, but the hardness value is largely decreased when the solution treatment temperature was 555° C., which is higher by 20° C. than the reference.

It was determined that when the solution treatment temperature increased up to the maximum upper limit of 555° C., secondary phases π-A18FeMg3Si6 and Mg2Si having a low melting point of 556 to 561° C. generated incipient melting, whereby defects were generated and accordingly the physical properties of the matrix tissues were rapidly dropped.

When the aging temperature was varied with the solution treatment conditions fixed, it was found that a change of matrix hardness was not large in an aging temperature range of 155 to 175° C., but when the aging temperature dropped to the maximum lower limit of 135° C., the matrix hardness was not largely increased even though aging treatment was performed for 4 hours. It is possible to determine that this is because the speed of growing into an Mg-based metastable precipitate phase (β″-Mg2Si or β′-Mg2Si) was low under a lower aging temperature condition such as 135° C., so junction of interfaces for strengthening the matrix was not completed by 4-hour aging.

Accordingly, the heat treatment and solution treatment temperature was set as 535° C. and the aging treatment temperature was set as 155° C.

EXAMPLE

Heat treatment, cooling, and aging processes were performed on an A356.2 material (refer to the following Table 1). A solution heat treatment step was performed for 6 hours at 535° C. and then aging treatment was performed for 2.5 hours at 155° C. Further, X-ray inspection was performed.

TABLE 1 A356.2 Reference Si 7 to 10 Fe 0 to 0.8 Cu 2 to 4 Mn 0 to 0.5 Mg 0 to 0.5 Cr 0 to 0.2 Ni 0 to 0.35 An 0 to 1 Sn 0 to 0.1 Ti 0 to 0.2 Pb 0 to 0.2 Na — Ca — Cd — Sr upto 250 ppm

Comparative Example 1

It was performed in the same way as the example, but the time of aging treatment was controlled to be below 2.5 hours and X-ray inspection was not performed.

Comparative Example 2

It was performed in the same way as the example, but aging treatment was performed for 4 hours and X-ray inspection was not performed.

Comparative Example 3

It was performed in the same as the example and aging treatment was performed for 4 hours.

Comparative Example 4

It was performed in the same way as the example, but heat treatment was performed for 8 hours and X-ray inspection was not performed.

The process conditions of the example and the comparative examples 1 to 4 are shown in the following Table 2.

TABLE 2 Aging Heat treatment treatment X-ray (535° C.) (155° C.) inspection Example 6 h 2.5 h Yes Comparative 6 h 2.5 h↓ No example 1 Comparative 6 h 4 h No example 2 Comparative 6 h 4 h Yes example 3 Comparative 8 h 4 h No example 4

<Result & Evaluation>

The mechanical properties of specimens according to the example and the comparative examples 1 to 4 are shown in the following Table 3.

TABLE 3 No. T/S (MPa) Y/S (MPa) EL (%) Example 1 276 175 24 2 263 159 16 3 266 166 16 4 280 170 19 5 266 199 17 6 277 200 15 Comparative 1 253 135 17 example 1 2 239 135 9 3 245 138 11 4 261 139 17 5 246 132 12 6 237 135 9 Comparative 1 271 165 13 example 2 2 259 156 14 3 272 169 12 4 267 163 14 5 284 177 11 6 263 171 10 Comparative 1 285 233 24 example 3 2 303 214 16 3 290 210 16 4 288 216 19 5 300 223 17 6 291 253 15 Comparative 1 289 206 10 example 4 2 293 211 17 3 254 208 7 4 287 205 11 5 285 209 9 6 301 212 14

Referring to Table 3, it was found that the relative strength was reduced by decreasing the solution treatment time, but tensile strength over 240 Mpa, which is required as reference, was secured in the example of the present disclosure, as compared with the comparative example 4. It was found that the solution treatment time was decreased but the cooling time was increased, whereby strength was improved using remaining heat and relatively high elongation was secured.

An aluminum alloy according to the manufacturing method of the present disclosure is characterized in that elongation is secured by reducing a solution treatment time, strength is secured by remaining heat by relatively increasing a cooling time, and elongation is excellent by controlling the cooling time and including Sr.

The features and technical advantages of the present disclosure were slightly broadly described for easy understanding of claims to be described below. It should be understood that the present disclosure may be implemented in other detailed ways by those skilled in the art without changing the scope or necessary features of the present disclosure. Therefore, the embodiments described above are only examples and should not be construed as being limitative in all respects. The scope of the present disclosure is defined by the following claims rather than the above detailed description, and all of changes and modifications obtained from claims and equivalent concepts should be construed as being included in the scope of the present disclosure. 

1. A method of manufacturing an aluminum alloy, comprising: a heating step of heating an aluminum alloy made of an aluminum alloy composite up to 500 to 560° C.; a solution treatment step of maintaining the heated aluminum alloy for 5 to 7 hours; a cooling step of cooling the solution-treated aluminum alloy for 15 seconds to 1 minute; and an aging step of age-hardening the cooled aluminum alloy for 2.5 to 4 hours at 140 to 180° C.
 2. The method of claim 1, wherein the aluminum alloy contains Sr.
 3. The method of claim 1, wherein the cooling is water cooling or air cooling.
 4. An aluminum alloy made by the method of manufacturing an aluminum alloy of claim
 1. 